The ban signals the end of Fuller's season, as it comprises the final five games of this season and the first one of the 2021 campaign. The speedy wideout is in the last year of his contract with the Texans.
Fuller said he was prescribed medication that he believed was permitted under the NFL's drug policy.
Texans cornerback Bradley Roby also announced he was handed a six-game suspension for using a banned substance.
The pair of Texans suspensions were linked to the same banned supplements, according to Aaron Wilson of the Houston Chronicle.
Fuller was enjoying a career year and, for the first time in his five seasons, hadn't missed any time with an injury.
As the No. 1 option in the Texans' passing game following the offseason trade of DeAndre Hopkins, Fuller had 53 catches, 879 yards, and eight touchdowns in 11 games, all career highs.
Fuller was the subject of trade speculation ahead of the deadline earlier in November. The Green Bay Packers were heavily linked to Fuller, but they reportedly couldn't agree on the level of compensation for a short-term answer.
Roby is in his second season with the Texans and has two years remaining on his contract. He had 35 tackles, one interception, and seven passes defended in 10 games.